Four sealed containers each hold a different pure substance at room temperature:
A. 17 g NH₃(g) (molar mass 17 g mol⁻¹)
B. 16 g O₂(g) (molar mass 32 g mol⁻¹)
C. 29 g N₂(g) (molar mass 28 g mol⁻¹)
D. 33 g CO₂(g) (molar mass 44 g mol⁻¹)
Which container contains about 3.0×1023 formula units? Give only the letter of the container.